Many oil and gas wells produce from two or more producing formations and have a separate string of production tubing for each formation produced. Many times the flow into the well bore, particularly in formations producing high pressure gas, is at high velocities and such streams impinging on the production tubing from a lower formation are extremely abrasive. Such production can erode a tubing string within relatively short periods of time and thereby provide undesired direct communication between producing formations. Such communication can prevent production from one of the formations and may result in thieving from the other.
Many different efforts have been made to solve this problem. U.S. Pat. No. 3,034,912 suggests multiple loose fitting rings of steel or plastic with projections thereof and surrounding the production tubing in the area of the formation performations to protect it from the abrasive action of the production streams impinging thereof. Such rings are proposed to be made of polyethylene or steel and rotate responsive to the streams impinging thereon to eliminate abrasion of the tubing. Such rings have not eliminated this type of abrasion and because of the necessity of the loose fitting of the rings could allow flow to impinge the tubing between the rings.
U.S. Pat. No. 3,365,000 discloses the use of a series of protective shields with a spring embedded in each shield to move the ring outward into the well bore when the protective shield is worn by the inflowing jets to allow the next higher shield to drop into protecting position. Such device admittedly only delays the erosion of the production tubing.
U.S. Pat. Nos. 4,141,386 and 4,028,796 suggest that this problem can be solved by surrounding the production tubing in the area of the upper formation perforations with an extended series of short cylindrical rings of cemented tungsten carbide. The same inventor in U.S. Pat. No. 4,211,440 claims that the practical solution in using such cemented tungsten carbide rings includes the introduction of a resilient biasing of the rings to allow freedom of movement of the rings relative to the tubing to permit handling and moving of the assembled joint without damage to the rings. These structures also wear since the cement matrix does not have the abrasion resistance that the tungsten carbide particles have. The rings when worn may break and fall into the well bore which can render subsequent movement of the production string difficult. Also, because of the flat abutment between rings high velocity jets can cut the tubing string through such abutments when aligned therewith. While stated by the patentee to be a commercial structure, the blast joint in use has not prevented damage to the tubing string.
Interconnecting heat insulation sheathing tiles have been proposed for pipes extending through furnaces as shown in U.S. Pat. Nos. 3,488,040 and 3,914,100. However, such structures are not suitable in a blast joint and they do not suggest the protective end rings and the arcuate interconnection between rings.